384 
ON THE DECAY OF STONE. 
contain appreciable quantities of the sulphate of lime having undoubtedly a similar 
origin.* 
A close examination into the circumstances attending the decay of stone at the Houses 
of Parliament invariably shows an increased liability to corrosion under the projecting 
eaves and mouldings, and at such sheltered parts of the stone surfaces as are usually 
covered with soot and dust, and are in a position to retain for the longest period the 
moisture absorbed during a season of rain. The plain ashlars are throughout very much 
less affected than the buttresses, gablets, and other elaborately carved and highly orna¬ 
mental portions of the work, which appear to be more assailable by reason of their rela¬ 
tively greater superficies. In many places the disintegrated stone exhibits white crystal 
of the sulphate of magnesia, which, alternately dissolving and recrystallizing in th 
pores of the stone, may be conceived to exert a disruptive action sufficient to accoun 
for the scaling and fracture of the dolomite which has been so often made the subject o 
complaint and regret. 
With the view of overcoming some of these difficulties I submitted a plan to the 
Royal Commissioners charged with inquiring into the decay of stone at Westminster, in 
May, 1861, which consisted in the application to the cleaned surfaces of the stone of an 
aqueous solution of superphosphate of lime,—a salt remarkable for its action in harden¬ 
ing the surfaces of chalk, Caen stone, or other calcareous buildiug stone to which it may 
be applied either by brushing or immersion, and which acts upon the carbonate of lime 
in the stone, giving rise to the formation of Bodeker’s salt (crystallized diphosphate of 
lime=2CaO,HO, P0 5 + 4aq.). My suggestion received a practical trial in a com¬ 
petition to which other five candidates were admitted by the Right Hon. the First Com¬ 
missioner of Her Majesty’s Works, in April, 1864, and in regard to the work executed 
on that occasion upon three faces of the Westminster Palace I fearlessly await the 
Government report. In the meanwhile, another promising scheme for the treatment of 
the decayed stone, especially applicable to dolomite, has been submitted by me to the 
notice of the First Commissioner, but this new proposal has not yet been selected for 
trial. It consists in the employment of baryta conjointly with the hardening salt, so 
that a base may be presented which is endowed with the power of destroying the soluble 
sulphate of magnesia in the pores of the stone, forming with it the remarkably insoluble 
sulphate of baryta, and, at the same time, engaging the magnesia in one of its most dif¬ 
ficultly soluble combinations. On a recent occasion I have applied this process on a 
small scale to some Caen stone facings at St. John’s Church, Woolwich, which were 
badly decayed. 
With reference to the application of the superphosphate to decayed Caen stone, I am 
able to refer to several successful examples of its use. In the year 1862 I applied the 
process upon some alms-houses forming part of Northfleet College, where the decay has 
been completely stopped. In 1864 I operated upon a window and buttress of St. John’s 
Church, Woolwich ; and in the following yeat the facade of the Grand Hotel, Brighton, 
was treated by my process. With respect to Portland stone, the earliest experiments 
were made at the Army Clothing Establishment, Woolwich, where in 1861 some de¬ 
cayed window-sills were treated, and with perfect success. I have some interesting 
results to record in connection with the treatment of Portland stone, which serve to 
illustrate the increased hardness and strength, and the diminished rate and capacity of 
water absorption attending the employment of the superphosphate. Small cubes of 
Portland stone, each 1-3 inch dimensions, were treated with the phosphate solution and 
left to dry in the air; these were then subjected to gradually increasing pressure, until 
crushed, between plates of lead in the American testing machine, at the Royal Gun Fac¬ 
tory ; and the breaking-weights of two precisely similar cubes of the native stone were 
at the same time carefully determined. The results were as follows:— 
* Caen stone, Northfleet College. 
Decayed exterior portion contained of sulphate of lime 3‘4 per cent. 
Interior of same stone (sound) „ „ nil. 
Caen stone, 8t. John’s Church, Woolw'ich. 
Scales of decayed stone contained of sulphate of lime 4'6 per cent. 
Interior portions (sound) „ „ „ nil. 
